netdev - Re: [PATCH v2 3/5] Bluetooth: hci_event: Add quirk to ignore byte in LE Extended Adv Report

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Message-ID: <CABBYNZLWc=2y0aVRc+_k_XzfJeEJkJ_ebaViqUybvaDY49p2_g@mail.gmail.com>
Date:   Wed, 7 Sep 2022 11:49:23 -0700
From:   Luiz Augusto von Dentz <luiz.dentz@...il.com>
To:     Sven Peter <sven@...npeter.dev>
Cc:     Marcel Holtmann <marcel@...tmann.org>,
        Johan Hedberg <johan.hedberg@...il.com>,
        "David S. Miller" <davem@...emloft.net>,
        Eric Dumazet <edumazet@...gle.com>,
        Jakub Kicinski <kuba@...nel.org>,
        Krzysztof Kozlowski <krzysztof.kozlowski+dt@...aro.org>,
        Paolo Abeni <pabeni@...hat.com>,
        Rob Herring <robh+dt@...nel.org>,
        Hector Martin <marcan@...can.st>,
        Alyssa Rosenzweig <alyssa@...enzweig.io>,
        asahi@...ts.linux.dev,
        "open list:NETWORKING [GENERAL]" <netdev@...r.kernel.org>,
        devicetree@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
        "linux-bluetooth@...r.kernel.org" <linux-bluetooth@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v2 3/5] Bluetooth: hci_event: Add quirk to ignore byte in
 LE Extended Adv Report

Hi Sven,

On Wed, Sep 7, 2022 at 10:10 AM Sven Peter <sven@...npeter.dev> wrote:
>
> Broadcom controllers present on Apple Silicon devices use the upper
> 8 bits of the event type in the LE Extended Advertising Report for
> the channel on which the frame has been received.
> Add a quirk to drop the upper byte to ensure that the advertising
> results are parsed correctly.
>
> The following excerpt from a btmon trace shows a report received on
> channel 37 by these controllers:
>
> > HCI Event: LE Meta Event (0x3e) plen 55
>       LE Extended Advertising Report (0x0d)
>         Num reports: 1
>         Entry 0
>           Event type: 0x2513
>             Props: 0x0013
>               Connectable
>               Scannable
>               Use legacy advertising PDUs
>             Data status: Complete
>             Reserved (0x2500)
>           Legacy PDU Type: Reserved (0x2513)
>           Address type: Public (0x00)
>           Address: XX:XX:XX:XX:XX:XX (Shenzhen Jingxun Software [...])
>           Primary PHY: LE 1M
>           Secondary PHY: No packets
>           SID: no ADI field (0xff)
>           TX power: 127 dBm
>           RSSI: -76 dBm (0xb4)
>           Periodic advertising interval: 0.00 msec (0x0000)
>           Direct address type: Public (0x00)
>           Direct address: 00:00:00:00:00:00 (OUI 00-00-00)
>           Data length: 0x1d
>           [...]
>         Flags: 0x18
>           Simultaneous LE and BR/EDR (Controller)
>           Simultaneous LE and BR/EDR (Host)
>         Company: Harman International Industries, Inc. (87)
>           Data: [...]
>         Service Data (UUID 0xfddf):
>         Name (complete): JBL Flip 5
>
> Signed-off-by: Sven Peter <sven@...npeter.dev>
> ---
> changes from v1:
>   - adjusted the commit message a bit to make checkpatch happy
>
>  include/net/bluetooth/hci.h | 11 +++++++++++
>  net/bluetooth/hci_event.c   |  4 ++++
>  2 files changed, 15 insertions(+)
>
> diff --git a/include/net/bluetooth/hci.h b/include/net/bluetooth/hci.h
> index cf29511b25a8..62539c1a6bf2 100644
> --- a/include/net/bluetooth/hci.h
> +++ b/include/net/bluetooth/hci.h
> @@ -263,6 +263,17 @@ enum {
>          * during the hdev->setup vendor callback.
>          */
>         HCI_QUIRK_BROKEN_ENHANCED_SETUP_SYNC_CONN,
> +
> +       /*
> +        * When this quirk is set, the upper 8 bits of the evt_type field of
> +        * the LE Extended Advertising Report events are discarded.
> +        * Some Broadcom controllers found in Apple machines put the channel
> +        * the report was received on into these reserved bits.
> +        *
> +        * This quirk can be set before hci_register_dev is called or
> +        * during the hdev->setup vendor callback.
> +        */
> +       HCI_QUIRK_FIXUP_LE_EXT_ADV_REPORT_EVT_TYPE,
>  };
>
>  /* HCI device flags */
> diff --git a/net/bluetooth/hci_event.c b/net/bluetooth/hci_event.c
> index 485c814cf44a..b50d05211f0d 100644
> --- a/net/bluetooth/hci_event.c
> +++ b/net/bluetooth/hci_event.c
> @@ -6471,6 +6471,10 @@ static void hci_le_ext_adv_report_evt(struct hci_dev *hdev, void *data,
>                         break;
>
>                 evt_type = __le16_to_cpu(info->type);
> +               if (test_bit(HCI_QUIRK_FIXUP_LE_EXT_ADV_REPORT_EVT_TYPE,
> +                            &hdev->quirks))
> +                       evt_type &= 0xff;
> +

Don't think we really need to quirk in order to mask the reserved
bits, according to the 5.3 spec only bits 0-6 are actually valid, that
said the usage of the upper byte is sort of non-standard so I don't
know what is broadcom/apple thinking that they could use like this,
instead this should probably be placed in a vendor command or even add
as part of the data itself with a vendor type.

>                 legacy_evt_type = ext_evt_type_to_legacy(hdev, evt_type);
>                 if (legacy_evt_type != LE_ADV_INVALID) {
>                         process_adv_report(hdev, legacy_evt_type, &info->bdaddr,
> --
> 2.25.1
>


-- 
Luiz Augusto von Dentz